Heat pipes are used in many space applications to conduct relatively large quantities of heat from a heat source, such as an electronic module to a heat sink, such as a heat radiation panel facing outer space. The advantage of the heat pipe in space applications is that it can conduct relatively large quantities of heat utilizing the latent heat of vaporization of a working fluid to extract heat from the heat source and releasing the latent heat of vaporization to a cold sink by condensing the vaporized working fluid. The details of heat pipes may be found in the textbook entitled "Heat Pipes," by P. D. Dunn and D. A. Reay, 4th Ed., published by Pergamon.
A heat pipe of the type to be used in spacecraft operation verification tests is shown in FIG. 1. The heat pipe 10 has an evaporator section 12 connected to a condenser section 16 by a connector section 18. A condensed working fluid 20 is collected in the condenser section and is returned to the evaporator section 12 by capillary action. Axial grooves such as grooves 34 shown in FIG. 3 transfer the condensed working fluid along the entire length of the heat pipe to replace the working fluid evaporated in the evaporator section. In this configuration, the condenser section 16 may be located almost anywhere relative to the evaporator section 12. The evaporator section 12 includes an evaporator mounting flange to which is attached a heat source (not shown) whose temperature is to be maintained within a predetermined temperature range. The evaporator mounting flange is thermally connected to the evaporator section and is at a temperature substantially the same as the evaporator section.
Condenser mounting pads 26 are connected to a heat sink such as a space heat radiator of the spacecraft which radiates heat to outer space.
In operation, the heat generated by a heat source is absorbed by the working fluid in the evaporator section 12 to vaporize the working fluid 20 and the vaporized working fluid travels inside the heat pipe to the condenser section 16 where it is cooled causing it to condense. The condensing of the working fluid releases the latent heat of vaporization which is radiated to outer space via the condenser mounting flanges. The condensed working fluid is transferred back to the evaporator section by capillary action where it is again evaporated, absorbing heat from the evaporator section. Because the primary heat transfer mechanism of a heat pipe is the latent heat of vaporization of the working fluid, there is only a small temperature difference between the temperature of the evaporated working fluid in the evaporator section and the temperature of the condensed working fluid in the condenser section.
In a substantially gravity-free space environment, the transfer of the working fluid over the length of the heat pipe is no problem in most cases. However, on the Earth's surface, gravity will inhibit the return of the working fluid above about 0.52 inches. This prohibits the testing of spacecraft functional and thermal systems in a gravitational field to verify the spacecraft's operating conditions.
Therefore, it would be advantageous to have a heat pipe which overcomes the shortcomings in the existing art.